I am using Standard Notes currently but I don’t want to pay 10$/month anymore.
Edit: Guys thank you all for your suggestions. Unfortunately I couldn’t find a one-size-fits-all approach like Google Keep or Apple Notes. I realized that we really dont have much choice as an open source community.
I decided to close my Standard Notes account and started using Gnome Text Editor (it does more than you think) with Syncthing. I am using Markor on my Android end. But it is not really a reliable solution since Syncthing consumes more battery than your average notes app and its GTK client is cumbersome. So even though my quest will continue, I am done for now.
Check out Logseq, or Obsidian, or Zettlr. They all use markdown as their base meaning you can transfer your notes anywhere if you don’t like the development of the app in the future. They all can be hosted on a Seafile instance which is a really good Delta-sync app that has encryption. I use https://luckycloud.de/en/ (seafile), which costs me 1 euro a month.
Thank you. Do you know other Seafile instances?
I only know of the ones on the seafile partner site. Luckycloud is the least expensive. https://www.seafile.com/en/partner/